1. The Field of the Invention
The present invention relates generally to devices useful in the diagnosis and treatment of speech impairment and in new language sound learning, and more particularly, but not necessarily entirely, to devices for determining the position of the tongue and determining the nasality of human speech.
2. Description of Related Art
The initiation of precise measurement technology and procedures in the nineteenth century opened the way to reproducible observations and rigorous explanatory theory in the sciences. Precise measures of tongue positions and movements were slow to develop, however, because the actions were concealed within the oral cavity and took place within a moist, chemically active environment. Phoneticians were left to personal impressions to infer what was happening as sounds were formed. Based on these inferences, they identified, inventoried, characterized, described, and classified sounds and their misarticulation. Hearing acuity, background noises, training and experience, and perceptual biases directly influenced these judgments.
In the late 1800s scientists discovered they could partially overcome their limited ability to confirm phonetic concepts by coating the palate with powder or other materials, having the person speak, then sketching or photographing where the tongue wiped the material off the palate during the sound spoken. This “palatographic” procedure was, however, restricted to single sound observations. Saying a second sound destroyed the wipe pattern. Dynamic speech remained physically inscrutable.
During the mid-1920s the sound spectrograph was invented. This instrument converted speech signals into time by frequency and intensity acoustic displays. The ability to display sound patterns brought a shift from physiology to acoustics in speech observations. Speech intelligibility, phonetic timing, coarticulation, and other phonetic entities were translated into this acoustic, listener oriented model. But the fact that acoustic output can infer only what might be happening in the mouth roused continually increasing concern. The need for information about actual articulator positions, fine cavity configurations, and three-dimensional movement patterns was increasingly recognized as imperative to both phonetic theory and practice.
The 1950s and 60s brought a serious search for ways to access the dynamic temporal and spatial qualities of speech production. X-rays, particularly cineradiology, opened this doorway. Analysis of these data was, however, fraught with problems related to key frame selection difficulties, slow and arduous hand tracing, noise from the recording camera that obscured acoustic details, bony structures occluding the tongue and other soft tissues unless radiopaque substances were used to define their margins, and, most importantly, damaging radiation that severely limited x-ray use. Computerized x-ray microbeam systems were introduced to reduce radiation by tracking lead pellets attached to articulatory structures. This extremely complex and expensive-to-implement technology reduced radiation but also limited the observations to the few points that could be tracked simultaneously.
In the 1980s magnetic resonance imaging (MRI) brought magnetic field, body-sectioning principles to speech studies. MRI's major limitations were that the subjects must be in a supine position, the measures were limited to a few samples per second, and soft tissue resolution was poor. Each of these factors compromised its use in dynamic speech observations.
Palatography was reintroduced in the 1960s using electronic technology to overcome the original single-sound observation limitations. Kusmin in Russia (Kuzmin, Yl (1962) Mobile palatography as a tool for acoustic study of speech sounds. Fourth International Congress on Acoustics, Copenhagen. Report G35) used paired electrodes to detect linguapalatal contact. Both members of his electrode pair had to be contacted simultaneously to complete the circuit. Several other investigators adopted this approach. Kydd and Belt (Kydd, W, Belt, D A (1964), Continuous palatography. Journal of Speech and Hearing Disorders. 29:489–492) used the tongue as the positive pole with twelve contact sensing electrodes on a pseudopalate in the system they developed. Both of these systems were fraught with serious signal detection and sensor-to-sensor saliva bridging problems.
In 1969 Fletcher, Berry, and Greer (see U.S. Pat. No. 4,112,596, granted Sep. 12, 1978 to Fletcher et al.) introduced the use of an AC signal to inject a body current that flowed to the tongue. When the tongue touched sensors on a pseudopalate placed in the mouth, the nonperceptable current continued through the tongue to them. The stronger current flow available in this procedure virtually eliminated saliva bridging and, in turn, significantly increased the potential density of the sensor sampling points. Precise definition of intraoral contact place, area and contour thus became feasible and was adopted by other investigators. The unique ability to identify and track articulation placement and movement and provide detailed information about dynamic action patterns at the precise locations and moments when critical speech production events were transpiring during rapid, intricate articulatory sequences was now available electropalatometrically.
The nasometer is a second major part of speech therapy and new language sound learning, next to the palatometer. Since its invention in the 1960s by Fletcher and his associates, the nasometer has become the most used instrument in the world for assessing and modifying abnormal nasal resonance (see U.S. Pat. No. 3,752,929, granted Aug. 14, 1973, to Fletcher). It detects, measures, and compares sound from the nose and mouth during speech. The measures are displayed as calculated “nasalance” acoustic intensity ratio scores within selectable bandwidths. “Nasogram” plots are used in differential diagnosis of nasality abnormalities from congenital disorders such as cleft palate, progressive diseases such as myasthenia gravis, and accidents that disrupt the ability to separate oral sounds from nasal resonance. The measures are also used to guide behavioral, surgical, and/or prosthetic intervention and to assess the amount and pattern of improvement.
In the original nasometer the plate that fits against the lip to separate sound from the mouth and nose had a “one shape fits all” curvature. If not prevented, sound could then leak between the microphone channels and contaminate the resulting nasalance scores. This problem has been corrected in our improved nasometer by using facial curvature data drawn from over 200 adults and children of different ages and ethnic origin. A set of interchangeable sound separation plates developed from these data effectively spans the human facial curvature range and optimizes inter-microphone sound isolation.
Our current invention, the Fonometer, brings the ability to tap a human's full capacity for fine tongue control and manipulation combined with new measurement technology and procedures. We have devised means of combining palatometry with other new instrumental devices that optimize the ability to define speech normality as well as diagnose and remediate speech abnormalities. Additionally, we have introduced means and procedures for using the Fonometer in tongue mobility testing and strengthening activities, in tongue driven external device control.
Despite the advantages of the prior art devices, the present invention provides numerous improvements described herein.